1. Field of the Invention
The present invention relates to an ultrasonic apparatus and a method utilizing ultrasonic waves for analyzing gases so as to measure trace amounts of gases in an air sample, and more particularly, to a new and improved ultrasonic apparatus and a method utilizing ultrasonic waves to measure amounts of gases in a gas/air mixture by comparing the sound velocity and acoustic attenuation of sound waves traveling through the gas/air mixture to the sound velocity and acoustic attenuation of sound waves traveling through air.
2. Background of the Invention
The measurement of trace amounts of gases mixed in air is needed in a number of different applications. For example, a portable field instrument can be used to detect and locate helium leaks from a component in which helium gas is used. In this regard, the instrument could be used for field inspection of potential leaks from a jet fuel-cell. While methods using ultrasonic waves have been used for characterizing gases, no ultrasonic instruments have been built specifically for detecting trace gases in a gas mixture. Moreover, inexpensive and portable gas analyzers are not readily available.
Another example where instruments are needed to measure trace amounts of gases in air is in the exhaust from a diesel engine. In such exhausts, unburnt carbon and volatile matter, such as hydrocarbons and inorganic species, are agglomerated to form particles of submicron size. These submicron size particles need to be monitored because the submicron particles are likely to cause health concerns due in part to their long suspension time in air. Diesel and compression ignition direct injection (CIDI) engines offer higher thermal efficiency than spark-ignited gasoline engines, but such engines tend to suffer from high emissions of NO.sub.X and particles. As a result, a significant amount of research has been directed to controlling the NO.sub.X and particulate matter (PM) emissions from light-duty vehicles. Consequently, low-cost and reliable emission sensors are needed in connection with the development of ways to control these emissions.
Optical techniques have been used for particulate monitoring. Measurements of light attenuation and scattering are generally used to determine particle concentration and size distribution, respectively. These optical techniques tend to be impractical for use in connection with the exhaust from a CIDI engine because of the complexity of the sensor design, the high costs of such devices and the hostile environment in the exhaust line of a CIDI engine where the gases need to be detected. In fact, such optical techniques tend to be limited to laboratory applications because of practical problems with such optical devices such as vibration effects on the light source and surface contamination of optical windows.
Yet another situation where detection and measurement of hydrogen gas is necessary is in connection with fuel cells. Fuel cells use energy more efficiently and produce less emissions that may pollute the environment. Those cells utilize hydrogen gas produced from alternate energy fuel to generate usable electrical energy which can be used to power automobiles or domestic appliances. However, those fuel-cells need to be closely monitored with respect to the flow of hydrogen to ensure the safe and efficient operation of the fuel-cell power system. Hydrogen sensors that have been typically used are based on electrochemical principles. However, these types of sensors cannot be used with such fuel-cell systems because of slow response time, interference from other reducing gases (e.g., CO), and lack of sensitivity to high concentrations of those gases. In this latter regard, typical hydrogen concentration in a fuel-cell system is around 38%. Thermal conductivity and mass spectroscopy also can be utilized in measuring such hydrogen gas. However, these types of technologies have certain draw backs. In the case of thermal conductivity, the measurements are flow rate dependent and in the case of mass spectroscopy, it requires an ionization source and a vacuum system.
Accordingly, it is an object of the present invention to provide a new and improved ultrasonic gas analyzer and a method to analyze trace gases using ultrasonic waves.
It is another object of the present invention to provide a new and improved ultrasonic apparatus and a method utilizing ultrasonic waves for analyzing gases so as to measure trace amounts of gases in an air sample by comparing the sound velocity and acoustic attenuation of the sound waves traveling through the gas/air mixture to the sound velocity and acoustic attenuation of the sound waves traveling through air alone.
It is still another object of the present invention to provide a new and improved ultrasonic apparatus and a method utilizing ultrasonic waves for analyzing gases so as to measure trace amounts of gases in an air sample by transmitting high frequency ultrasonic wave pulses through a gas sample flowing through an acoustic cavity and analyzing the speed of and attenuation of the pulsed waves traveling through the gas samples.
It is yet another object of the present invention to provide a new and improved ultrasonic apparatus for measuring trace amounts of gas in air that is low in cost, rugged and highly sensitive so as to be capable of detecting trace amounts of certain types of gases in an air sample.